Of particular interest to me, of late, is a quasi-psychological diagnosis; Posttraumatic Relationship Disorder. I say it is quasi-psychological because it is not an official diagnosis, and it is not necessarily something that is widely endorsed by the field. Honestly, I do not know. However, I will say that this is a diagnosis that makes much sense to me. Google the symptoms for Posttraumatic Stress Disorder...PTSD involves witnessing, hearing of, or being involved in a traumatic incident, having some sort of remembrances of the trauma through dreams, or flashbacks, or intrusive thinking, having these memories triggered by sights or sounds, or places, or smells, or a touch, etc, finding the memories to be so distressing that one takes advanced steps to avoid having these remembrances, and emotional fallout from having this problem...disconnecting from others, having mood problems, having behavior problems, feeling disconnected or avoidant, etc etc.
In my experience, it is the case that some people, when they go through a relationship breakup, experience much of these symptoms. The loss of a relationship can be so intensely painful, and so intensely devastating, that the person may develop a form of Posttraumatic Stress Disorder specific to this type of trauma. In this disorder, the person may be brought to their knees, so to speak, by the emotional devastation caused by the loss of the relationship. They may feel as if the other person died, or that they died, after the end of the relationship, because of the extreme distress they experience. They may think obsessively about the loss, and may have trouble keeping it off their mind. They may attempt to get it out of their mind, and they may become very good at knowing what is likely to trigger a memory. For instance, a car that is red, just as the ex's was, and is more or less the same shape, may trigger flashbacks of the relationship complete with visuals, sounds, and feelings. Activities that you participated in with the other may now cause devastating feelings of despair or pain. Sleep may be interrupted by horrible dreams of the past, when you were together with that person. Your mood may become constantly anxious, or depressed, or both. You may struggle with maintaining a stable mood, and may have trouble staying focused on what you should be focusing on.
It can take weeks, or months, or even sometimes years for a person to finally get to the point that they no longer have debilitating symptoms in this area, in my opinion. What helps, just as with your typical trauma disorder, is work on taking away the power of the trauma, work on improving your sense of mastery over possible similar future trauma, and work on regaining you emotional equilibrium. There is hope.